1. Field of the Invention
The present invention relates to an optical wavelength demultiplexer mainly for use in wavelength-division-multiplexed optical communications.
2. Description of the Related Art
Heretofore, optical wavelength demultiplexers mainly for use in the art of wavelength-division-multiplexed optical communications comprise a single optical fiber, a collimator lens, a diffraction grating, and a one-dimensional array of photodetectors. In the optical wavelength demultiplexers, the optical fiber is positioned at the focal point of the collimator lens. Light emitted from the optical fiber is converted by the collimator lens into parallel light that is applied to the diffraction grating which is Littrow-mounted. The diffraction grating demultiplexes the light with its chromatic dispersion capability and applies the demultiplexed light rays to the collimator lens, which focuses the light rays on the photodetectors in respective channels.
Another type of optical wavelength demultiplexer comprises a concave diffraction grating, a single optical fiber disposed at the focal point of the concave diffraction grating, and a one-dimensional array of photodetectors. Light emitted from the optical fiber is reflected and demultiplexed by the concave diffraction grating into light rays that are focused on the photodetectors in respective channels.
If the number of demultiplex channels is to increase, then the photodetector array will require an increased number of photodetectors. Since the photodetector array will have an increased width, it will be difficult to design aberrations of the collimator lens.
One optical wavelength demultiplexer provides a single input capability. If an optical wavelength demultiplexer system with two or more input capabilities is needed, then it is necessary to provide as many optical wavelength demultiplexers as the required number of input capabilities. Since each of the optical wavelength demultiplexers has the diffraction grating and the collimator lens, or the concave diffraction grating, which is expensive, the overall optical wavelength demultiplexer system is highly expensive.